I've taken a view that when the world was destroyed by The Great Flood, it meant the "known world". Which at the time was not very big. Thus the Flood of Gilgamesh could have been the Great Flood. It's like God creating the world in seven days. As if one of God's days are 24 hours.
Genesis 6:17
And behold, I Myself am bringing floodwaters on the earth, to destroy from under heaven all flesh in which is the breath of life; everything that is on the earth shall die.
That seems to indicate the entire earth was flooded, if one concludes that if there were other parts of earth they had life forms on them also.
You're free to believe Gilgamesh over Scripture. Of course, there's a lot more evidence for the veracity of Scripture than Gilgamesh....